Disk drive decreasing a settle delay based on speed that a settle parameter adapts
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of tracks, and control circuitry operable to seek the head to a target track and settle the head on the target track during a settle time, adapt a settle parameter used to settle the head on the target track, access the target track after an access delay, and decrease the access delay based on a speed that the settle parameter adapts.
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Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the velocity of the actuator arm as it seeks from track to track.
Because the disk is rotated at a constant angular velocity, the data rate is typically increased toward the outer diameter tracks (where the surface of the disk is spinning faster) in order to achieve a more constant linear bit density across the radius of the disk. To simplify design considerations, the data tracks are typically banded together into a number of physical zones, wherein the data rate is constant across a zone, and increased from the inner diameter zones to the outer diameter zones. This is illustrated in
The prior art disk format of
In the embodiment of
In one embodiment, when the control circuitry 21 seeks the head 16 to a target track, one or more settle parameters are used to settle the head onto the target track during a settle interval. In an example described below, the settle parameters may comprise a magnitude of a sinusoid that estimates a repeatable runout (RRO) of the disk 18. The sinusoid may be used to generate feedforward compensation values so that the head follows the RRO while settling onto the target track (and while tracking the centerline of the target track). In one embodiment, it may take several seeks (e.g., a hundred seeks) for the settle parameters to converge. That is, during the settle interval of each initial seek the settle parameters are adapted, and after a number of seeks, the settle parameters converge toward optimal values. At the beginning of the learning seeks, the settle parameters are typically suboptimal, and therefore an access delay associated with accessing the track (write or read) is increased to allow more time for the head to settle onto the track, thereby avoiding off-track writes and or slipped revolutions. This is illustrated in
In one embodiment, the control circuitry 21 measures the speed that the settle parameter adapts according to:
speed[k]=(1−α)speed[k−1]+α(p[k]−p[k−1])
where k−1 and k represent a beginning and end of the interval, α is a scalar, and p is the settle parameter. The above equation operates to filter out outliers in the adapting speed measurements so that the access delay decreases without significant transients. However, the above equation is optional, or may be modified into any suitable filtering function.
Referring again to the example of
In one embodiment, the initial adapting delay may equal the initial access delay, but the final adapting delay may be greater than the final access delay. For example, in
In one embodiment, the settle parameter may continue adapting during the access operation, but is initialized with the value saved at the end of the adapting delay. As described above, initializing the settle parameter based on the end of the adapting delay of the previous seek operation may help track a peak in an adaptation profile of the settle parameter as illustrated in the example of
In one embodiment, the tracks of the disk may be banded together to define a plurality of zones, wherein a different value may be used for the settle parameters for each zone. That is, there may be multiple sets of settle parameters where each set corresponds to a zone, and each set may be adapted when the control circuitry seeks the head into the respective zone. In one embodiment, the control circuitry may adapt the settle parameters of a zone only when the seek length to reach the zone exceeds a threshold. That is, the settle parameters may exhibit a particular characteristic (such as the overshoot peak in
Any suitable control circuitry may be employed to implement the flow diagrams in the embodiments of the present invention, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain steps described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into an SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the steps of the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
Claims
1. A disk drive comprising:
- a disk comprising a plurality of tracks;
- a head actuated over the disk; and
- control circuitry operable to:
- (a) seek the head to a target track and settle the head on the target track during a settle time;
- (b) adapt a settle parameter used to settle the head on the target track;
- (c) access the target track after an access delay;
- (d) decrease the access delay based on a speed that the settle parameter adapts; and
- (e) repeat (a) through (d) at least once.
2. The disk drive as recited in claim 1, wherein the control circuitry is further operable to measure the speed that the settle parameter adapts by measuring a difference between the settle parameter over an interval.
3. The disk drive as recited in claim 2, wherein the control circuitry is further operable to measure the speed that the settle parameter adapts according to:
- speed[k]=(1−α)speed[k−1]+α(p[k]−p[k−1])
- wherein:
- k−1 and k present a beginning and end of the interval;
- α is a scalar; and
- p is the settle parameter.
4. The disk drive as recited in claim 2, wherein the interval spans at least part of a single settle time for a single seek.
5. The disk drive as recited in claim 4, wherein the interval spans at least part of multiple settle times for multiple seeks.
6. The disk drive as recited in claim 1, wherein the settle parameter comprises a magnitude of a sinusoid that estimates a repeatable runout (RRO) of the disk.
7. the disk drive as recited in claim 1, wherein the control circuitry is further operable to:
- adapt the settle parameter over an adapting delay of the settle time;
- save the settle parameter after the adapting delay of a first settle time of a first seek;
- further adapt the saved settle parameter over the adapting delay of a second settle time of a second seek; and
- decrease the adapting delay based on the speed that the settle parameter adapts.
8. The disk drive as recited in claim 7, wherein the adapting delay substantially equals the access delay.
9. A method of operating a disk drive comprising, the disk drive comprising a head actuated over a disk comprising a plurality of tracks, the method comprising:
- (a) seeking the head to a target track and settle the head on the target track during a settle time;
- (b) adapting a settle parameter used to settle the head on the target track;
- (c) accessing the target track after an access delay;
- (d) decreasing the access delay based on a speed that the settle parameter adapts; and
- (e) repeating (a) through (d) at least once.
10. The method as recited in claim 9, further comprising measuring the speed that the settle parameter adapts by measuring a difference between the settle parameter over an interval.
11. The method as recited in claim 10, further comprising measuring the speed that the settle parameter adapts according to:
- speed[k]=(1−α)speed[k−1]+α(p[k]−p[k−1])
- wherein:
- k−1 and k present a beginning and end of the interval;
- α is a scalar; and
- p is the settle parameter.
12. The method as recited in claim 10, wherein the interval spans at least part of a single settle time for a single seek.
13. The method as recited in claim 12, wherein the interval spans at least part of multiple settle times for multiple seeks.
14. The method as recited in claim 9, wherein the settle parameter comprises a magnitude of a sinusoid that estimates a repeatable runout (RRO) of the disk.
15. the method as recited in claim 9, further comprising:
- adapting the settle parameter over an adapting delay of the settle time;
- saving the settle parameter after the adapting delay of a first settle time of a first seek;
- further adapting the saved settle parameter over the adapting delay of a second settle time of a second seek; and
- decreasing the adapting delay based on the speed that the settle parameter adapts.
16. The method as recited in claim 15, wherein the adapting delay substantially equals the access delay.
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Type: Grant
Filed: Aug 9, 2011
Date of Patent: Oct 22, 2013
Patent Publication Number: 20130038962
Assignee: Western Digital Technologies, Inc. (Irvine, CA)
Inventors: Mingji Lou (Corona, CA), Xiuli Guo (Irvine, CA), Orhan Beker (Aliso Viejo, CA)
Primary Examiner: Peter Vincent Agustin
Application Number: 13/206,354
International Classification: G11B 5/596 (20060101);